Closed Canopy Plots Research Articles

Soil and Nutrient Cycling Responses in Riparian Forests to the Loss of Ash (Fraxinus spp. L) from Emerald Ash Borer (Agrilus planipennis, Fairmaire)

Emerald ash borer (EAB) is an alien invasive species that is spreading across Canada and the United States killing ash trees. In riparian forests where ash may be abundant; loss of ash can induce significant structural changes; including the creation of canopy gaps; changes in light penetration; expansion of ground vegetation; and alteration of soil nitrogen and carbon cycling. In 2014 and 2015, we examined the effects of EAB-caused gaps in riparian forests on soil nutrient dynamics. Two sites with different infestation timelines, a “new” site (mortality in past 2–3 years) and an “old” site (infested 10 years previous) were selected to determine temporal differences in effects of canopy gaps created by ash loss on litterfall, herbaceous ground vegetation, and soil nutrient cycling. Within both sites, plots with clustered dead ash (canopy gap plots—CG) were paired with nearby plots of full canopy and no ash (canopy closed plots—CC), and differences between paired plots determined. Total litterfall was observed at all sites but was only significant at the new infestation site. Reductions in leaf litter deposition in CG plots resulted in reduced N and C flux to the forest floor but soil C and N concentrations, and nitrogen mineralization rates, were not significantly different between CG and CC plots. Nitrate concentration in soil solution was significantly greater in CG plots compared to CC plots at the new infestation sites but showed the opposite trend at the old infestation sites. Herbaceous ground vegetation biomass was significantly greater (up to 10×) in CG plots than in CC plots. Overall, despite changes to riparian forest canopy structure and litterfall, there was no significant difference in soil nutrient cycling between EAB-induced canopy gaps and closed canopy plots after 10 years, suggesting a high resilience of riparian forest soils to EAB infestation

Dung longevity influences the fate of endozoochorically dispersed seeds in forest ecosystems

Many studies show large discrepancies between the potential (studied in the greenhouse) and realized (studied in the field) effects of endozoochory. The influence of environmental conditions on the fate of endozoochorically dispersed seeds and subsequent plant establishment is still not well understood. We addressed this issue by studying the viable seed content of the dung of European bison ( Bison bonasus L.) by means of seedling germination in the greenhouse and in two forest habitats in Białowieża Primeval Forest. The number of seedlings and the number of plant species that emerged from 1 L of feces were positively correlated with dung longevity. Generative shoots were produced by plants only in coniferous forest. Their number was positively correlated with dung longevity and with light availability. Germination of seeds from bison feces was higher in coniferous forest than in deciduous forest but did not differ between open- and closed-canopy plots within the same habitat. We conclude that (i) seed germination and plant establishment after endozoochorous dispersal is influenced by dung longevity; (ii) the number of generative shoots produced by endozoochorously dispersed plants is influenced by dung longevity and light availability; (iii) seeds of some plant species, present in dung, stay viable for at least 3 years.

Bryophyte community response to silvicultural opening size in a managed northern hardwood forest

We examined the influence of group-selection opening size on the structure and composition of bryophyte communities in a managed northern hardwood forest. We quantified bryophyte communities in 49 group-selection openings, ranging in size from 200 to 1460 m 2, 2 years following overstory removal. Bryophyte communities in forest openings were compared to those observed on 20 closed canopy reference plots in the surrounding forest matrix. Both the overall importance ([relative percent cover + frequency]/2) of bryophytes as a group and total percent cover of bryophytes were significantly lower ( P < 0.005) in openings compared to closed canopy plots. However, a continuous decline in bryophyte importance was not observed with increasing opening size. Opening creation resulted in pronounced shifts in community composition. In general, species that occurred in both the forest matrix and openings displayed high substrate fidelity across treatments. Collectively, our results suggest that while openings were clearly hostile environments for some species, they probably provide important habitat for and may facilitate the persistence of some disturbance-adapted bryophyte species.

Impacts of forest gaps on soil properties and processes in old growth northern hardwood-hemlock forests

We examined the influence of treefall gaps on soil properties and processes in old growth northern hardwood-hemlock forests in the upper Great Lakes region, USA. We found significantly greater solar radiation, soil moisture contents and soil temperatures in gaps compared to adjacent closed canopy plots. Gaps had significantly less exchangeable base cations (K, Ca, and Mg) compared to forest plots in the upper mineral soil (0–25 cm). Gaps also had significantly more dissolved organic N and extractable nitrate at depth (25–50 cm), indicating increased nutrient leaching in gaps. In-situ N mineralization was significantly greater in gaps and edge plots compared to forest plots. We found significantly greater potential N mineralization (measured in the laboratory at 25°C and 40% water holding capacity) in forest compared to gap plots. Microbial biomass N was significantly greater (ca. two-fold) in the gap edge compared to both gaps and closed forest. Using principal component analyses we found that edge plots were positively correlated with all principal components, indicating increased in-situ and potential N mineralization, microbial biomass N, soil NO3− and NH4+, and soil organic matter. The gap edge may be a region of optimal microclimate and substrate to enhance microbial biomass and activity within these forest ecosystems.

Extant and potential vegetation of an old-growth maritime Ilex opaca forest

The extant and potential (seed bank) vegetation of a rare maritime holly forest on Fire Island, New York was described to assess whether treefall gaps act as a mechanism for the persistence of the species composition of this plant community over time. The Sunken Forest overstory is dominated by Ilex opaca, Amelanchier canadensis and Sassafras albidum. A survey of canopy gaps indicated canopy openings compose 11.3% of the land within the Sunken Forest (16 ha). The composition and density of the seed bank were described using the emergence method. Germination from soil samples placed in the greenhouse was monitored over 2 years. Sixteen species germinated with an average propagule density of 215±41 germinants per square metre. An early successional species (Rhus copallinum) dominated the seed bank, but the late-successional, shade-tolerant I. opaca was also present. Though only one species in the seed bank did not appear in the current vegetation, species abundance differed between vegetation strata. The mean cover and density of the ground-layer flora were higher beneath treefall gaps than closed canopy. Sapling density did not differ between the two canopy conditions, but the dominant species differed with A. canadensis occupying several closed canopy plots and P. serotina saplings appearing more often in gap plots. Most of the dominant canopy species are present in the seed bank and ground layer but are not present in the shrub and sapling layer, with the exception of A. canadensis. Current (2002) sapling density is lower than three decades ago for all species except P. serotina, which is now the dominant woody species in the Sunken Forest understory. The results of this study indicate that if the cause of the sapling reduction is lessened or removed, the characteristic species of the overstory of this unusual plant community may rebound and redevelop a sapling and shrub layer akin to that present before the increase in Odocoileus virginianus on the island.

Succession, Sapling Density and Growth in Canopy Gaps Along a Topographic Gradient in a Second Growth East Tennessee Forest

Canopy gaps in a second growth forest in East Tennessee were studied to document succession, sapling species partitioning in individual gaps and possible sapling adaptations for gap colonization. Ten gaps (64 to 309 m2, mean = 186 m2) and four closed canopy plots (200 m2 each) were surveyed. All trees were identified and located, extension growth of the leader stem of saplings (n = 933) was measured and diameter at breast height (dbh) of trees > 3 m tall (n = 504) was measured. Sapling composition in gaps was dominated by Fagus grandifolia Ehrh., Acer rubrum L. and A. saccharum Marsh., indicating that several species in the current canopy, dominated by Quercus spp, Pinus spp, Liriodendron tulipifera L. and F. grandifolia Ehrh., will eventually be replaced. There was little evidence of within gap partitioning either between the north and south portions of gaps or between their centers and edges, perhaps due to a history of instability in disturbance regimes. All three dominant sapling species showed significantly greater extension growth in gaps than in closed forest. Acer rubrum grew significantly less in gaps than A. saccharum. Under closed canopy this result was reversed, suggesting that while A. saccharum may be better adapted to using gaps, A. rubrum may grow better beneath the canopy.

The Influence of Undergrowing Acanthus ilicifolius on Mangrove Seedling Establishment.

We considered the influence of Acanthus ilicifolius on mangrove seedling establishment. A. ilicifolius is one of a shade-intolerant species and often forms dense thickets when forests are disturbed. The number of seedlings and saplings of mangroves were larger in open canopy plots than closed canopy plots in the sites without A. ilicifolius. On the other hand, there were few seedlings and scarcely saplings in both open and closed canopy plots in the site with A. ilicifolius. Usually, open canopy plots with sufficient light should be a good place for regeneration of mangrove species. However, mangrove seedling establishment seems to be prevented by A. ilicifolius, because the thickets make dark condition on forest floor in open canopy plots. Moreover, long viviparous propagules may hardly move through A. ilicifolius thickets. The thickets of A. ilicifolius will prevent mangroves from regenerating by seeds.

Growth and form of Douglas-fir adjacent to persistent vine maple gaps in southwestern British Columbia

Vine maple is distinct in its ability to prevent conifer establishment and create persistent gaps. The goal of our research was to determine the influence of persistent vine maple gaps on the morphology, basal growth, and the productivity of Douglas-fir within a temperate rainforest. On 10 paired plots, gap size, Douglas-fir crown and bole size, site chronologies and site productivity were examined in a 75-year-old, second-growth stand. Median gap size was 80 m 2. Douglas-fir on the gap edge had 61% greater growing space, 182% larger crowns and 46% larger boles than Douglas-fir in the forest matrix. Crown expansion into the gap and the long-term presence of the canopy gap has resulted in crowns on the side of the tree adjacent to the gap that were 62% wider and 36% deeper than closed canopy crowns, resulting in crown volumes of Douglas-fir adjacent to gaps that were 182% greater than for trees in the closed canopy. Annual basal area increments (BAI) for Douglas-fir on gap plots exceeded BAI for Douglas-fir in the closed canopy by as much as 70%. Site index was significantly higher on gap plots when compared to closed canopy plots, indicating vine maple may play an important role in the long-term fertility of forest ecosystems where it is a dominant component in the understory. Site BA and recent BA productivity did not significantly differ between gap and canopy plots. Persistent gaps in Douglas-fir stands offer an opportunity for silviculturists to incorporate biodiversity and stand structural objectives into silvicultural systems without significant trade-offs in timber production.

Relationship of Heliothis zea predators, parasitoids and entomopathogens to canopy development in soybean as affected by Heterodera glycines and weeds

AbstractThe influence of canopy development in soybean on the survival of corn earworm, Heliothis zea (Boddie) (Lepidoptera: Noctuidae), egg and larval stages and population dynamics of arthropod fauna were evaluated in field trials during 1986–88 in eastern North Carolina. Soybean canopy size decreased as soybean cyst nematode, Heterodera glycines Ichinohe (Nematoda: Heteroderidae), initial population densities increased. Plant species composition of the soybean canopy was affected by weed population densities. Mortality of H. zea larvae due to parasitism and infection with entomopathogens was greater in closed canopy and (or) weedy soybeans than in very open and (or) weed free soybeans. Predation and parasitism of corn earworm eggs were similar across nematode and weed density treatments. Natural enemy populations increased to highest levels during July in closed canopy and (or) weedy soybeans, coinciding with availability of largest prey population reservoirs. A delay in colonization of very open and (or) weed free soybeans by beneficial arthropods until mid to late August allowed greater H. zea larval survival than in closed canopy and (or) weedy soybeans. Arthropod species richness was generally greatest in closed canopy and (or) weedy soybeans during mid to late July, with differences becoming nonsignificant in August and early September. Mean and maximum ambient temperatures were higher and relative humidities lower in open canopy than in closed canopy plots. These conditions were less favorable for development of pathogens and natural enemies.